Require TLS 1.2 for HTTPS Connections was a critical update in Summer ’19 and is enforced in Winter ’20
on October 25, 2019. To maintain the highest security standards and promote the safety of your data,
Salesforce is disabling the older Transport Layer Security (TLS) 1.1 encryption protocol. All inbound
connections to or outbound connections from your Salesforce org must use TLS 1.2. Verify that your
browser access, API integrations, and other Salesforce features are compliant with TLS 1.2.
https://help.salesforce.com/s/articleView?id=release-notes.rn_networks_tls_cruc_enforced.htm&release=222&type=5